Electromagnetic coil.



K. S. JOHNSON.

ELECTROMAGNETIC COIL. APPLICATION FILED DEC.10| HT- 1 ,297,858. Patented Mar. 18,1919.

Slal/on B S/a/ion A /n yen/0K Kenn 2/77 5. Jon/won STATES PATENT OFFICE.

KENNETH S. JOHNSON, OF JERSEY CITY, NEW JERSEY, ASSIGNOR TO WESTERN ELEC- TRIC' COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

To all whom it may concern I Be it known that I, KENNETH S. JoHNso-N, acitizen of the United States, residing at Jersey City, in the county of Hudson and State of New Jersey, have invented certain new and useful Improvements in Electromagnetic Coils, of which the following is a full, clear, concise, and exact description.

This invention relates to electrical transformers and in particular toa type which is efficient with currents of high frequency but is inefficient with currents of low frequency. v

In the field of electrical transmission of messages. there is considerable need for a sending of telephone and telegraph .,mes-

sages. In-such systems it is desirable to transmit current of a frequency of from approximately 400 to 2,000 cycles but'to suppress currents of a lower frequency, as for example, the 16 cycle ringing current ordinarily used and the low frequency Morse currents. In various other circuits,. it is also highly advantageous to provide means for preventing the transmission of all currents except those within a given frequency range.

Heretofore ithas largely been the practice to suppress or filter out the currents of undesired frequency by means of resonant shunts or by certain combinations of inductances and capacities. This method although efi'ective requires the use of considerable apparatus especially when it is desired to suppress currents of-comparatively low frequency, suchfor example as those required in signaling on telephone lines and.

the sending of Morse signals. Under such conditionsthe capacities required are such as to practically preclude their use in portablesets and in othercases the cost is prohibitive for commercial reasons.

It is therefore the object of the present invention to provide a means for suppressing currents oflow frequencyv and at the same time permit thetransmission of currents of high frequency, such apparatus be- ELECTROMAGNETIC COIL.

Patented Mar. 18,1919.

Application filed December 10, 1917. Serial No. 206,476.

ing compact, low in. weight and cheap to manufacture.

In accordance With a. feature of this invention there is provided an electromagnetic coil, the magnetic circuit of which com prises a plurality of sections, of a material having high permeability and low hysteresis and eddy current losses, these sections being joined by yoke pieces of a material having high hysteresis and eddy current losses. Upon each of the former sections are wound a primary and secondary winding, the corresponding windings in each case being joined together in series opposed to each other.

The invention is illustrated in the accompanying drawing, in which Figure 1 illustrates a structure embodying this invention;

and Fig. 2 illustrates a simplified circuit in which a structure of this type may be employed.

The magnetic circuit of this coil comprises core sections 4 and 5, composed of laminations of a material having high permeability and low hysteresis and eddy current losses, silicon steel having been found particularly suitable for this purpose. The core sections 4: and 5 are joined by the solid 'yoke pieces 66, of a material having high hysteresis and eddy current losses, such for example as wrought iron, cast iron or hardened steel. These yoke pieces are held in place by means of the screws 7-7 and the washers 8-8. The windings comprise a.

prnnary Winding P---P and a secondary winding SS each of which is equally andsymmetrically wound on the core sections 4 and 5, the portions of each winding being so connected that the fluxes generated by a 3 flow of current therein, are in a direction to oppose and neutralize each other. In response to'the flow of alternating currents of low frequency the series opposing connection of P-P as well as that of.S-S will make the transformer of practically zero efliciency, Whilein response to currents of high frequency the effective permeability of the yoke pieces. 66 will be but slightly higher than that of air, hence the device at this frequency will act as two separate transformers connected in series. The loss of effective permeability with increasing frequency is due chiefly to the effect of the eddy .currents in the yoke pieces and to a lesser degree to hysteresis losses in the yoke pieces.

to eddy currents increases apin proportion to the square of ondary windings are each connected in series opposing to each other. The loss, due to hysteresis currents, increases somewhat faster than in direct proportion to the frequency and hence aids in further decreasing the effective permeability of the yoke pieces.

Referring now more particularly to Fig. 2 there is shown a composite line suitable for the simultaneous sending of telephone and telegraph messages, the customary condensers and impedance coils being eliminated and the transformer or repeating coil eminvention being provided. at each telephone station to. prevent any disturbance from the telegraph circuit reaching the telephone sets. While onlytwo sets are shown connected to the line it will be obvious that other sets may be provided as desired. As illustrated, the telephone apparatus at each station consists of a transformer or repeatingcoil of the type-shown in Fig. 1 and havin its primary winding PP con-' necte between the line and ground. The

bodying this terminals of the secondary winding SS an ordinary local battery telephone set consisting in this case of the induction coil .9, battery 10, transmitter 11, receiver 12 and hook-switch 13. The telegraph apparatus prises a grounded source of energy 14, telegraph key 15, and relay 16, connected to the line wire as shown. "Itwill be understood that at each station and associated with the are connected directly to relay 16 there will be a local circuit comprising a telegraph sounder andsjoattery not shown in the drawing. The signaling current of low frequency traversing the line wir as a result of. the opening and closing of the key 15 will flow through the primarywindings P P at each telephone station, but due to the construction of the transformeras already described'similar currents will not be induced into the secondary winding SS hence no disturbancewill be'create at this over the telephonic windings on each at each station com:

station due to the operation of the telegraph apparatus. On the other hand'in response to alternating currents of telephonic frequencies traversing the l1ne wire the transformer functions efliciently, the high fretogether in series opposing.

2. An electromagnetic coil comprising a plurality of cores composed of a material having high permeability and low hysteresis and eddy current losses, yoke pieces mechanically separating and magnetically joining said 'cores, said yoke pieces being composed of a material having high hysteresis and eddy current losses, and a plurality of of said cores, corresponding windings on the different cores being connected together in series opposing.

3. An electromagnetic coil comprising a plurality of laminated cores mechanically separated from each other and magnetically connected by solid yoke pieces, and a primary and a secondary winding on each core, said primary windings being connected together in series opposing and said secondary windings being connectedtogether in series opposing.

4. In a device for selectively transmitting electrical waves, a plurality of coils adapted to be included in a transmission line, a magnetic core for'each of said coils, and a magnetic connection between said cores, said connection offering high reluctance to rapid changes of flux in said cores and low reluc-- tance to slow-changes of flux in said*cores.

5. In a device for selectively transmitting ioo electrical waves, a plurality of coils, a magnetic core for each of said coils, and a magnetic connection between said cores, said connection being composed of a materialh'aving high hysteresis and eddy current losses adapted to permit the interchange between said cores of slowly changing .flux and to prevent the interchange of rapidly changing In witness whereof, I hereunto subscribe m'y-name this 5th day of December, A. D 1917. v

KENNETH sJoHnsou. 

